Dust formation/generation and spreading have been a continuing cause of environmental and health concerns. Dust spreading is a common problem found on transportation thoroughfares, mines, mineral transportation and storage piles, tailings storage, power plant stock piles, construction sites, unpaved roads and other areas where particulates may be dispersed into the air and onto surrounding surfaces. Dust generation is where dust, small particles of materials, is formed. For example, in the processing and handling of inorganic granules such as roofing granules, small particles are generated. Where these particles are small (<30 mm) enough, they become dust. Generally, dust is airborne or capable of becoming airborne.
The spreading and generation of dust particles present an environmental (air quality) issue that must be dealt with by the manufacturer, the distributors and the end-users. A common method that has been used to suppress and control the dust consists of merely wetting down the area with water.
Wetting with water is environmentally benign and low cost. However, this method has a very limited duration, as once the water evaporates, the effect no longer exists. Moreover, because of its limited duration, a tremendous amount of water resources are wasted. In attempts to improve upon this, hygroscopic salts such as magnesium chloride or calcium chloride are often added to the water in attempts to enhance the surface moisture retention. Although more effective, these compositions result in high usage of salts and have undesired environmental impacts. Another method used to control dust generation is spraying the area with an oil. Although quite effective at suppressing dust generation for extended periods of time, this method is not as environmentally friendly. In addition to possible environmental issues, it may pose a significant long term clean-up problem and even potential health concerns. Moreover, the oil treated substrates may adhere to vehicles attempting to travel over the treated surfaces, generating unwanted clean-up, excess wear on mechanical equipment, and accelerated breakdown of the treated surfaces. Oils additionally may change the properties of the coated surface, for example oils may cause an unwanted change in color. Synthetic polymers have also been used to abate dust spreading by changing the physical properties of the soil or dusty surfaces. The polymeric molecules can possibly coat and agglomerate the dust particles together, making them heavier and therefore reduce the spreading of the dust particles significantly.
Most of the reported polymeric dust suppressants are polyvinyl acetate and vinyl acrylic polymer latex. See, for example, U.S. Pat. No. 6,372,842. Aqueous solutions are also described, for example in U.S. Pat. Nos. 5,194,174; 4,417,992 and 4,801,635.
Other examples include those described in EP01234106A2; U.S. Pat. No. 3,900,611; U.S. Pat. No. 3,763,072; WO 2005/121272 and U.S. Patent Application Publication No. 2007/073590.
However, the performance relationship to the flexibility of the polymeric chains (as measured by their glass transition temperature, Tg) was never revealed. Actually, all reported polymer based dust suppressants are with relatively high glass transition temperatures (Tg >0° C.). These relatively high Tg polymeric dust suppressants may provide adequate performance in the static applications, however, their performance in dynamic applications may be poor because the film formed on the surface is too brittle to be kept intact under the dynamic conditions, such as moving and tumbling, as well as heavy traffic. Specifically, dynamic conditions include heavy traffic on unpaved roads, materials on a conveyor belt and crushing, and in the roofing granule process.